The primary objective of this program project is to increase knowledge of the health effects of smokeless tobacco, particularly its effects on oral and dental disease and on various physiologic measures. Three projects are proposed: (1) a study of smokeless toboacco use and clinically and histopathologically defined oral and dental disease in professional baseball players, which will include collection of prevalence data on smokeless tobacco use over three years and a 2 year follow-up study of clinical findings in smokeless tobacco users and nonusers; (2) a study of physiologic effects of smokeless tobacco use, including blood pressure, heart rate, cholesterol, high density lipoproteins, and white blood count; and (3) a study to investigate whether specific viruses known to play a role in epithelial neoplastic processes are involved in oral lesions associated with smokeless tobacco use. A core component will relate to three projects and will include the following functions: a) scientific leadership; b) administrative support; c) data management and statistical analysis; d) protocol training; e) cotinine validation; and f) histopathology review. Professional baseball players are an ideal study population because of their high rates of smokeless tobacco use, their public visibility, and their role model status for young males. Taken together, the projects proposed here have the potential to contribute significantly to future efforts to educate dental health professionals and the lay public about the health effects of smokeless tobacco use.